The use of a truck-mounted articulated boom for moving a workperson to an elevated work position is well known. A bucket carrier is so mounted to the arm of the boom as to maintain a vertical orientation irrespective of the angle of the boom. This may be accomplished by securing the bucket to a shaft coupling which is freely axially rotatable with respect to the boom and providing a boom-carried levelling system to rotate the bucket shaft in a sense that compensates for motion of the arm of the articulated boom. The bucket itself may also be pivotably movable in a horizontal plane, for adjusting the position of the person carried in the bucket relative to the boom and a work jib mounted to the boom, by means of a bucket rotation drive system between the bucket shaft and the bucket carrier.
To assist the workperson in the bucket carrier, there is usually provided a work jib near the end of the boom. The jib assembly comprises a jib which is slidable and lockable within a sleeve that is pivotably mounted to the boom, proximate the bucket carrier. Hydraulic driving means may be provided for extending and rotating the jib within a vertical plane. There may also be provided a hydraulically driven winch, if needed for the handling of materials, mounted to the boom or to the jib sleeve.
Two jib assemblies generally of the type disclosed herein are described in Canadian patent No. 1,198,691 issued Dec. 31, 1985 to Amador Hydraulics Services Limited and U.S. Pat. No. 4,838,381 issued Jun. 13, 1989 to Posi-Plus Technologies Inc.
The Amador jib assembly comprises a jib and a speed reducer which includes a worm gear concentric with the bucket shaft and freely rotatable relative thereto and a hydraulic motor-driven worm for rotating the worm gear to effect rotation of the jib in the vertical plane.
In the articulated boom jib assembly disclosed in the Posi-Plus patent, the jib member has an attachment sleeve element secured thereto, which is in turn secured to a drive gear coupling element in toothed engagement with the output drive gear of a planetary gear reducer securable inside the boom. The Posi-Plan arrangement is intended to address a disadvantage of the Amador construction, by supporting the jib closer to the boom to reduce stress on the gear coupling caused by the load associated with the jib assembly and on the bucket support shaft.
However, none of the prior art jib assemblies is entirely satisfactory for use in the tightly spaced and hazardous environment of power distribution lines, particularly when the operator requires in addition to the functions of jib rotation and jib extension a powered winch for raising and lowering materials to the elevated work station. The prior art devices all employ bulky winches which have hydraulic hose and winch cable routing problems.
In conventional arrangements including a hydraulic motor-powered winch mounted to the arm at the boom or to the jib, the associated hydraulic hoses lie outside the jib and have to "sweep around" with the jib to the extent that the jib is rotated in use. This restricts rotational freedom and particularly precludes having usable tools at both ends of the work jib. To varying degrees, the hydraulic winch and hose configurations in known jib assemblies also restrict bucket rotation in the horizontal place and can impede access to the jib controls from the "passenger" bucket, in a two bucket carrier.
The cable routing problems of the prior art referred to above stem from the rotation axis of the winch being displaced from the rotation axis of the jib, so that the cable is not in alignment with the groove of the pulley sheave in the tip of the jib. In time, this can lead to chafing and even cutting of the winch cable.
It is, accordingly, an object of the present invention to provide an improved jib assembly having a compact configuration of components which allows a high degree of freedom in the rotation of the jib in the vertical plane and minimal obstruction of the rotational adjustment of the bucket carrier in the horizontal plane, to provide the workperson carried in the bucket with a preferred positioning of the jib for conductor and other material handling.
It is a further object of the invention to provide an improved jib assembly for use with a boom carried by an aerial device, the boom arm having a bucket carrier for a workperson on a freely rotatable shaft extending through the boom, wherein rotation of the jib is effected by hydraulic chain drive means including a jib rotation output sprocket coaxial with the bucket shaft and freely rotatable in relation thereto, affording a relatively compact configuration for the jib assembly.
It is a further object of the invention to provide an improved jib assembly for use with a boom carried by an aerial device as aforesaid, further comprising a compact and light winch concentric with both the bucket support shaft and the jib rotation output sprocket.
It is a further object of the invention to provide an improved jib assembly for use with an articulated boom, wherein jib rotation is effected by compact chain-and-sprocket drive means fixed to the boom tip, and comprising a compact winch coaxial with the output sprocket of the jib rotation drive means and winch rotation drive means also fixed to the boom tip, so that the winch cable is lined up with the sheaves of a pulley at one end of the jib.